1. Field of the Invention
This invention relates to pneumatic tires, and more particularly to an improvement in traction performance and ride comfortability of a pneumatic tire being mounted onto, for example, a construction vehicle or the like and running on good and bad roads inclusive of relatively soft road surface, relatively hard road surface, and the like.
2. Related Art Statement
As this type of the tire, there have hitherto been known pneumatic tires as shown in FIGS. 8 to 10. In pneumatic tires 1 and 2 of FIGS. 8 and 9, land portions 6 defined between grooves 5 extending in the widthwise direction of the tire are arranged on a surface portion 3a of a tread 3 at an approximately a constant pitch (P.sub.1 or P.sub.2) in the circumferential direction of the tire to form an uneven pattern (hereinafter referred to as pattern simply) on the surface portion 3a of the tread 3. These tires 1 and 2 mainly attach importance to the traction performances and in fact have good traction performance. When the tires 1 and 2 are run on a relatively soft road surface under loading, the unevenness of the tread 3 is absorbed by such a road surface, so that vibrations are less during running and there is no problem on ride comfortability. On the other hand, when these tires are run on a relatively hard road surface, vibrations are generated by the unevenness of the tread 3 to cause the problem on ride comfortability. However, such a problem is regarded to be unavoidable because the traction performance is important.
In order to solve this problem, as shown in FIG. 10, the groove is eliminated from the central portion 3b of the tread 3 to form a land portion 6a continuously extending in the circumferential direction. In this case, however, the drastic solution of ride comfortability can not yet be said though the ride comfortability is improved to a certain extent. On the other hand, since the land portion 6a is formed in the central portion 3b, the volume of the groove reduces and the mud brushing performance is degraded to sacrifice the traction performances, so that there is naturally caused a problem of reducing the tractability.